1. Field of the Invention
This invention relates to a vinyl chloride resin composition characterized by containing a co-ground mixture of at least one member selected from the group consisting of an organic phosphoric ester compound and its metal salt and a grinding aid.
2. Description of the Related Art
Vinyl chloride resins are used in a wide range of applications; for they are inexpensive and can have their hardness adjusted easily by using a plasticizer.
However, vinyl chloride resins have a light/heat stability problem. It is noted that a vinyl chloride resin is liable to decompose primarily due to dehydrohalogenation during heat molding processing or in use. Hence there have been attempts to improve stability of vinyl chloride resins by addition of a metal compound as a main stabilizer in combination with various co-stabilizers.
A problem is that some of the co-stabilizers have poor compatibility with a vinyl chloride resin only to yield moldings with deteriorated physical properties such as transparency. Another problem is that a poorly dispersible co-stabilizer can cause sudden blackening in spots on the resulting moldings, which is called zinc burning.
Patent Document: 1 discloses an antimicrobial composition for polymeric materials that contains a phosphoric ester compound or a metal salt thereof. The publication gives no mention nor suggestion that the phosphoric ester compound or its metal salt is effective in improving transparency of polymers.
Patent Document: 2 teaches that a phosphoric ester metal salt is usable as a nucleating agent for crystalline resins. A nucleating agent is to become crystalline nuclei of a crystalline resin and produces its effect as being retained inside resin crystals. There is no suggestion of using a phosphoric ester metal salt for noncrystalline polymers.
Patent Document: 1JP-A-2001-220464Patent Document: 2JP-A-58-1736